Undertale, Underfell, Underswap Lemons

*UPDATE: All ranges of Undertale smut/lemons (mostly lemons by this point) No longer one shot. Contains multiple one-shots, and occasionally two-shots. Male readers can request a character x male reader :)
Underfell Sans x Female Reader. Smut or a Lemon *shrugs* might be a one shot (if no one wants more I guess)